1. Field of the Invention
This invention relates to an image forming device which uses field emission electron sources for use in a cold cathode lamp, a fluorescent display tube, a backlight for a liquid crystal device, a field emission display, and the like. In particular, the invention relates to an image forming device provided with cathode electrodes, gate electrodes, and focusing electrodes of wire structure, as well as a getter of greater surface area.
2. Description of the Related Art
In recent years, much research and development has been made on field emission electron sources for releasing field emission electrons under a high electric field, with the expectation of their application to flat panel displays, i.e., field emission displays (FEDs).
Well-known among those field emission type electron sources are field emission sources of pyramidal shape, made of the metal material that is used for the conical electron sources formed of a high melting-point metal material through the evaporation method by C. A. Spindt et al. (U.S. Pat. No. 3,665,241)
Such pyramidal field emission electron sources are fabricated in a self-aligning fashion by making holes of the order of 1 xcexcm and then using the evaporation method. Recently, 10-odd-inch FEDs using such pyramidal field emission electron sources have been announced to receive much attention.
Meanwhile, an image forming device using carbon nanotubes have been disclosed lately. A carbon nanotube, having a nested structure of cylindrically wound graphite layers, was found by Iijima et al. (S. Iijima, Nature, 354, 56, 1991)
As disclosed in Japanese Patent Laid-Open Publication No. Hei11-162383, such an FED using carbon nanotubes (see FIGS. 11(a) to 11(c)) has been constituted by forming electrode lines and insulators on a substrate.
On a substrate 101 there are formed an electrode wiring layer 102 and an insulating film 103 on which substrate-side ribs 104 are arranged at predetermined intervals. An electron emitter portion 105 is formed on the insulating film 103 between the substrate-side ribs 104 and an electron extracting electrode 106 is formed on the substrate-side ribs 104. A front-end glass substrate 107 and the substrate 101 are spaced from each other by the perpendicularly crossing substrate-side ribs 104 and a front-end rib 108 by a predetermined distance. A light-emitting portion 110 comprising a fluorescent material is formed in a region sandwiched by the front-end ribs 108 on the inner surface of the front-end glass substrate 107, where the a metal back film coats surface of the light-emitting portion.
Moreover, as described in Japanese Patent Laid-Open Publication No.Hei 10-50240, a conventional FED has had a getter arranged in the vicinities of luminant layers on its face plate so as to provide uniform gas absorption for the entire interior of the envelope.
Nevertheless, the FEDs using such field emission electron sources of pyramidal shape, made of the conventional metal material have had the problem that micromachining of the order of 1 xcexcm is required and the individual field emission electron sources cannot be controlled uniform in shape.
In addition, the operating vacuum level as high as 10xe2x88x929 Torr and breakage of the field emission electron sources due to the ion sputtering by residual gas have been another problem.
Meanwhile, the FED using conventional field emission electron sources made of carbon nanotubes has had the problem of how to subdivide the carbon nanotube electron sources for micropixels and to control the orientation of the carbon nanotubes.
Furthermore, the pyramidal, the carbon-nanotubed, and other conventional FEDs have had the problem that the number of steps for forming and patterning thin layers is increased by the formation of a cathode, gate insulator, gate electrode, interlayer insulation film, focusing electrode, and the like. These FEDs have also had the problem that the getters for maintaining the FED operating vacuum level can only be arranged to the envelope rims, precluding efficient evacuation.
Moreover, the conventional FED having the getter arranged in the vicinities of the luminant layers on its face plate has had the problem that an increase in getter surface area for the sake of enhancing absorption efficiency brings about a drop in intensity.
The present invention has been achieved in view of the foregoing problems, and an object thereof is to provide an image forming device for driving field emission electron sources capable of low-vacuum operation, high in ion impact resistance, and controlled in orientation, under X-Y addressing through electrode lines of simple and low-cost configuration. Another object of the present invention is to provide an image forming device in which a getter capable of efficient degassing is arranged to cope with greater areas.
To solve the foregoing problems, the present invention in a first aspect provides an image forming device comprising: a first electrode line formed on a supporting substrate; an electron source array formed on the first electrode line; a second electrode line arranged to be orthogonal to the first electrode line; and an insulator for providing electric insulation between the first electrode line and the second electrode line. Here, at least either one of the first electrode line and the second electrode line has a wire structure, and the insulator is a first vacuum gap. This simplifies the structure and the fabrication steps of the image forming device.
In a second aspect, the present invention provides an image forming device in which: the second electrode line has the wire structure; the second electrode line is composed of a plurality of electrode lines each having the wire structure; and a pixel includes a plurality of electron source arrays mentioned above. This simplifies the gate electrode structure in an X-Y addressable image forming device, and omits the gate insulator.
In a third aspect of the present invention, the first electrode line is provided with a region onto which the electron source array is selectively formed. Thereby, the electron source array is selectively integrated onto a desired pixel area in the image forming device.
In a fourth aspect of the present invention, the aforesaid region contains a metal catalyst selected from the group consisting of cobalt, nickel, iron, and an alloy of the metal catalyst, while the electron source array contains one selected from the group consisting of diamond, diamondlike carbon, and carbon nanotubes. This makes the image forming device high in ion impact resistance and capable of low-vacuum operation, as well as enhances the electron source array in orientation controllability.
In a fifth aspect, the present invention provides an image forming device in which the aforesaid region has a multilayer structure of a metal anodic oxide film, an anodic oxidation stop layer, and the metal catalyst. This means enhanced adhesion of the electron source array, reduced dust production in the fabrication processes, and improved reliability of the image forming device.
In a sixth aspect, the present invention provides an image forming device having the metal anodic oxide film made of aluminum, so as to control the packaging density in the electron source array of the image forming device and the sizes of the individual electron sources.
In a seventh aspect, the present invention provides an image forming device in which both the first electrode line and the second electrode line have a wire structure. This simplifies the structure and the fabrication steps of an X-Y addressable image forming device.
In an eighth aspect of the present invention, the supporting substrate and the first electrode line are isolated from each other by a second vacuum gap. Thereby, it becomes possible to arrange a getter on the supporting substrate, maintaining the image forming device in a high vacuum and increasing its panel area.
In a ninth aspect of the present invention, the getter is made of a carbon material selected from the group consisting of graphite, carbon nanotubes, and fullerenes. This enhances the gas absorption efficiency inside the image forming device and improves reliability.
In a tenth aspect of the present invention, a third electrode line is arranged over the second electrode line, and the third electrode line is formed in a wire structure. This avoids crosstalk in an image forming device and simplifies the structure and the fabrication steps of an image forming device with focusing electrodes.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.